38 U.S.C. § 1153 : Veterans’ Benefits — Compensation For Service-Connected Disability Or Death — General Compensation Provisions — General Benefits — Aggravation

A preexisting injury or disease will be considered to have been aggravated by active military, naval, or air service, where there is an increase in disability during such service, unless there is a specific finding that the increase in disability is due to the natural progress of the disease.